U.S. patent number 4,237,886 [Application Number 05/892,200] was granted by the patent office on 1980-12-09 for electrode to be used in contact with a living body.
This patent grant is currently assigned to Natsuo Uchiyama, Sony Corporation. Invention is credited to Tadasu Kawashima, Isoji Sakurada.
United States Patent |
4,237,886 |
Sakurada , et al. |
December 9, 1980 |
Electrode to be used in contact with a living body
Abstract
An electrode, or grounding pad for contact with a living body
comprises a conductive substrate of a textile having conductive
fibers, a conductive adhesive layer containing carbon fibers for
contacting the surface of the living body and being affixed to the
conductive substrate, and an electrical connection to the
conductive substrate.
Inventors: |
Sakurada; Isoji (Kanuma,
JP), Kawashima; Tadasu (Utsunomiya, JP) |
Assignee: |
Sony Corporation (Tokyo,
JP)
Natsuo Uchiyama (Tokyo, JP)
|
Family
ID: |
26345788 |
Appl.
No.: |
05/892,200 |
Filed: |
March 31, 1978 |
Foreign Application Priority Data
|
|
|
|
|
Apr 2, 1977 [JP] |
|
|
52-37821 |
Jan 31, 1978 [JP] |
|
|
53-10506[U] |
|
Current U.S.
Class: |
606/32; 252/511;
607/152 |
Current CPC
Class: |
A61B
18/16 (20130101); A61N 1/04 (20130101) |
Current International
Class: |
A61B
18/16 (20060101); A61B 18/14 (20060101); A61N
1/04 (20060101); A61B 017/36 () |
Field of
Search: |
;128/303.13,2.6E,2.1E,404,410,411,416-418,DIG.4,639-641,644,783,798,802,803
;252/510,511 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
13888 |
|
Apr 1970 |
|
AU |
|
122258 |
|
Feb 1972 |
|
DK |
|
50-18702 |
|
Feb 1975 |
|
JP |
|
Primary Examiner: Cohen; Lee S.
Attorney, Agent or Firm: Eslinger; Lewis H. Sinderbrand;
Alvin
Claims
We claim:
1. An electrode for electrically contacting a surface of a living
body comprising:
a conductive substrate of a textile having conductive fibers
constituting more than 15% by weight of said textile;
a conductive adhesive layer for contacting the surface, said
adhesive layer being affixed to said conductive substrate and
including a mixture of carbon fibers and a resin in which said
carbon fibers have a length of 0.2 to 6 mm and a diameter of 1 to
20 .mu.m, and are contained in said adhesive layer in an amount
ranging from about 2 to 30% by weight relative to the remainder of
said adhesive layer;
each of said substrate and said adhesive layer having a specific
resistance of less that 100.OMEGA. cm; and
means forming an electrical connection to said conductive
substrate.
2. An electrode according to claim 1; wherein said conductive
substrate includes carbon fibers.
3. An electrode according to claim 1; wherein said conductive
substrate includes conductive metal fibers.
4. An electrode according to claim 1; wherein said conductive
substrate has a thickness of approximately 50 to 1000 .mu.m and
said adhesive layer has a thickness of approximately 25 to 200
.mu.m.
5. An electrode according to claim 1; wherein said resin in the
adhesive layer has a base polymer a major part of which consists of
an acrylic or methacrylic acid ester of an alcohol having 1 to 8
carbon atoms in its molecule, and a minor part of the base polymer
of said resin consists of a first vinyl compound having a
crosslinkable functional group.
6. An electrode according to claim 5; wherein said acrylic or
methacrylic acid ester is substituted by a second vinyl compound in
an amount of less than 20 parts by weight of said second vinyl
compound for each 100 parts by weight of said acrylic or
methacrylic acid ester.
7. An electrode according to claim 6; wherein the first and second
vinyl compounds are copolymerized in the base polymer in the range
of 0.25 to 3.0 parts by weight of said vinyl compounds for each 100
parts by weight of the total amount of said base polymer.
8. An electrode according to claim 5; wherein said base polymer has
a glass transition temperature of -85.degree. to 0.degree. C. and
an average molecular weight of 50,000 to 500,000.
9. An electrode according to claim 5; wherein said base polymer is
cross-linked by a cross-linking agent to produce said adhesive
layer.
10. An electrode according to claim 1; wherein said adhesive layer
includes natural rubber.
11. An electrode according to claim 1; wherein said means for
forming an electrical connection includes a cylindrical member
having a flanged end and penetrating said adhesive layer and said
substrate with said flanged end being against said adhesive layer,
and an interconnection member affixed to the other end of said
cylindrical member and being in electrical contact with said
conductive substrate.
12. An electrode according to claim 11; wherein said
interconnection member is soldered to said conductive
substrate.
13. An electrode according to claim 11; wherein said
interconnection member is crimped on, and thereby affixed to said
cylindrical member.
14. An electrode according to claim 11; wherein said flanged end of
said cylindrical member has an insulated cover thereon to prevent
electrical contact of said cylindrical member with said
surface.
15. An electrode according to claim 11; further comprising a
flexible insulating material affixed to said conductive substrate
on the side of said substrate opposite said adhesive layer.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to electrodes to be used in contact with a
living body such as the human body, and more particularly to
electrodes to be used as grounding pads opposite active surgical
electrodes during surgery.
2. Description of the Prior Art
The conventional electrode or "grounding pad" is contacted with the
thigh, back or other portions of the human body at a location
opposite an active surgical electrode or electro-surgical pencil
with blade. An electric current is passed from the active electrode
to the grounding pad through the human body to provide a cutting or
coagulating action at selected locations.
In the conventional electrode or grounding pad, a gauze containing
a physiological saline solution is affixed on a metal plate of
lead, stainless steel or the like, having a lead wire extending
therefrom. The electrode is contacted with the human body through
the gauze. Unfortunately, such conventional construction of the
electrode gives rise to various disadvantages. For example, due to
poor flexibility of the electrode, contact with the curved surfaces
of a human body can become uneven or the saline solution may dry
with extended usage, both of which conditions can result in uneven
current density over the contact area and the danger of burns. In
addition, miniaturization of such an electrode, for application to
limited areas, is difficult. Further, problems with sanitization of
the electrode can develop.
Another known construction of the conventional electrode or
grounding pad, is of a so-called conductive jelly type, wherein a
sponge containing conductive jelly is affixed to an inner surface
of a sponge-like substrate to form the electrode. Contact with the
human body is effected through the conductive jelly, while the
sponge-like substrate is affixed to the human body through adhesive
material coated on the marginal portion of the inner surface
thereof. A lead wire is connected with the sponge containing the
conductive jelly. Although an opposed electrode or grounding pad of
this type is at least initially relatively well contacted with the
human body so that unevenness of electric current density is
relatively decreased, there is still a danger of burns being
suffered due to uneven contact when the conductive jelly is dried
after being used for a long time. In addition, special steps are
required for sanitizing the electrode and preventing water
evaporation therefrom, such as, enclosing the electrode in a
sanitary bag or sak. Such additional procedure adds complication
and expense to the production and use of this type of
electrode.
In still another known type of electrode or grounding pad, a metal
foil of aluminum or the like is directly contacted with the human
body, and the metal foil is attached to a substrate of larger size
than the foil, and the substrate is affixed to the human body
through adhesive material coated on the marginal portion of the
inner surface thereof. Unfortunately, electrodes of this type are
liable to wrinkle due to poor flexibility of the metal foil. As a
result, contact with the human body is not uniform and uneven
current distribution results with the danger of burns occurring.
Also, this type of electrode is not suitable for surgical
operations on children because of its relatively large size.
In a conventional conductive adhesive, metal particles, such as, of
copper or silver, are dispersed in a resin, and this adhesive can
be applied to a tape. Unfortunately, the specific resistance of
such an adhesive is liable to become uneven or unstable, because it
is higher than that of the conductive particles contained in the
resin and the particles are not surely contacted with the electric
conductor. For this reason, when such a conductive adhesive tape is
attached to a living body and to the lead wire, a relatively low
resistance value cannot be obtained unless the adhesive tape is
attached under strong pressure to cause the metal particles to be
forcibly exposed on the surface of the adhesive layer to produce
good conductivity. Accordingly, when the conventional adhesive is
applied as an opposed electrode or grounding pad for an
electric-surgical pencil, or the like, there is a danger of causing
a concentration of an electric current density if the pressure on
the adhesive is weak or uneven.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an
electrode, or grounding pad, for contact with a living body, and
which forms uniform contact with the latter to provide even current
distribution across the area of contact.
Another object of the invention is to provide an electrode or
grounding pad which will not dry out with extended use and thereby
cause an uneven current distribution and the danger of burns.
Still another object of the invention is to provide an electrode or
grounding pad, as aforesaid, which is flexible and can conform to
various surface shapes on a living body.
A further object of the invention is to provide an electrode or
grounding pad, as aforesaid, which can be formed in a small size
for contact with limited surface areas.
It is a further object of the invention to provide an electrode or
grounding pad, as aforesaid, which ensures good current
distribution over the surface area of the electrode by providing
sufficient electrical contact between the electrode and the lead
wire affixed thereto.
It is a still further object of the invention to provide an
electrode or grounding pad, as aforesaid, having good mechanical
strength.
In accordance with an aspect of this invention, an electrode or
grounding pad for electrically contacting a living body comprises a
conductive substrate made of a textile having conductive fibers, a
conductive adhesive layer for contacting a surface of the living
body, said adhesive layer being affixed to said conductive
substrate and containing carbon fibers, and means forming an
electrical connection to said conductive substrate.
In accordance with a feature of the invention, the adhesive layer
includes a mixture of carbon fibers and a resin, wherein the carbon
fibers may have a length of 0.2 to 6mm and a diameter of 1 to 20
.mu.m and are continued in said adhesive layer in an amount ranging
from about 2 to 30% by weight relative to the remainder of the
adhesive layer.
In accordance with another feature of the invention, both the
substrate and the adhesive layer have a specific resistance, or
resistivity, of less than 100.OMEGA. cm., and the conductive
substrate has a thickness of 50 to 100 .mu.m which the adhesive
layer has a thickness of 25 to 200 .mu.m.
In accordance with another feature of the invention, the adhesive
layer includes a resin having a base polymer, a major part of which
consists of an acrylic or methacrylic acid ester of an alcohol
having 1 to 8 carbon atoms in its molecule, and a minor part of
which consists of a vinyl compound having a crosslinkable
functional group. In one embodiment, the acrylic or methacrylic
acid ester is substituted by another vinyl compound in an amount of
less than 20 parts by weight of the other vinyl compound for each
100 parts by weight of the acrylic or methacrylic acid ester. In
another embodiment, the vinyl compounds are copolymerized in the
base polymer in the range of 0.25 to 3.0 parts by weight of said
vinyl compounds for each 100 parts by weight of the total amount of
the base polymer.
In accordance with a further feature of the invention, the means
forming an electrical connection to the conductive substrate
includes a cylindrical member having a flanged end and penetrating
said adhesive layer and said substrate with said flanged end being
at the side of said adhesive layer, and an interconnection member
affixed to the other end of said cylindrical member and being in
electrical contact with the conductive substrate. Such
interconnection member may be soldered to the conductive substrate
and crimped on the cylinderical member so as to be affixed to the
latter. The cylinderical member may desirably have an insulating
cover of the flanged end thereof to prevent electrical contact
between the cylindrical member and the surface of the living body.
The electrode may further have flexible insulating material affixed
to the conductive substrate on the side opposite the adhesive
layer.
The above, and other objects, features and advantages of the
invention, will be apparent in the following detailed description
of illustrative embodiments to be read in connection with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of a conventional electrode, or
grounding pad;
FIG. 2 is a cross-sectional view of an electrode or grounding pad,
according to the present invention;
FIG. 3 is a graph showing the frequency characteristics of
electrodes of the kind shown on FIG. 2 with various conductive
substrates;
FIGS. 4A and FIG. 4B are graphs showing the specific resistance for
several conductive substrates used in electrodes according to this
invention;
FIG. 5 is an exploded perspective view of the several elements of
the electrode shown in FIG. 2;
FIG. 6 is a cross-sectional view similar to FIG. 2, but showing
solder material impregnated into a conductive substrate; and
FIG. 7 is a front elevational view showing the manner in which the
electrode of FIG. 2 may be used.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Before proceeding with the description of the invention, reference
will be made to FIG. 1 in which a conventional electrode of the
conductive jelly type is shown to comprise a sponge-like substrate
1, an adhesive layer 2, an insulating frame 3 affixed to the
sponge-like substrate 1 through the adhesive layer 2, a stainless
steel plate 4 located inside the frame 3, a conductive lower
electrode element 6 which is inserted from the lower side of the
substrate 1 into a hole 5 formed therein and in the plate 4, a
conductive upper electrode element 7 which is mechanically united
with an extruded portion 6a of element 6, and a doubling or back-up
plate 9. To unite the upper electrode element 7 with the lower
electrode element 6, the element 7 is placed over the extruded
portion 6a of element 6 and crimped, as at 8, against the element
6. The frame 3 is filled with a foam sponge 10 containing
conductive jelly which extends over an area larger than that
occupied by plate 4. The sponge 10 and the conductive jelly therein
is contacted with a flanged end 6b of lower element 6 and with the
stainless steel plate 4.
In the electrode of FIG. 1, the stainless steel plate 4 has a
larger surface area than the flanged end 6b of the lower electrode
element 6. The plate 4 thereby is able to reduce the electrical
resistance of the electrode and spread the electric current over a
larger surface area to prevent concentrations thereof.
Unfortunately, the sponge 10 is insufficient for maintaining a
suitable electric contact and becomes relatively bulky because it
must be formed relatively thick in consideration of the volume
decrease that occurs upon drying of the conductive jelly.
Electrical contact between the elements 6 and 7 is also limited as
these elements are only electrically connected with each other at
the crimped region 8. The conventional electrode of FIG. 1
additionally suffers from poor mechanical strength due to poor
attachment of its element 7 to the substrate 1. Further, there is a
danger of burns occurring due to the drying of the conductive jelly
when used for a long time.
Referring now to FIG. 2, it will be seen that an electrode or
grounding pad 20 according to this invention is there illustrated
to generally comprise a conductive substrate 11, a conductive
adhesive layer 12, upper and lower electrode elements 7 and 6,
respectively, a ring-shaped solder layer 14, a washer 19, a
sponge-like substrate 1, an adhesive layer 2, a lead wire 15 with a
terminal plate 16, and an insulating cover or cap 13.
The electrode or grounding pad 2, of FIG. 2 is particularly
characterized by the conductive substrate 11 and the conductive
adhesive layer 12. The conductive substrate 11 includes a textile
having conductive fibers of suitable composition and the conductive
adhesive layer 12 is affixed to the conductive substrate and
contains carbon fibers for providing electrical conductivity
therethrough. Further details of the conductive substrate 11 and
adhesive layer 12 are given below.
The conductive substrate 11 and the conductive adhesive layer 12
have a penetrating hole 18 therethrough. The lower electrode
element 6 extends through the penetrating hole 18 and has a flanged
end 6b at the lower, or contact, side of adhesive layer 12. The
washer 19 is located around the lower electrode element 6 and
between the flanged end 6b and the conductive adhesive layer 12.
The insulating cap or cover 13 is located over the flanged end 6b
of electrode 6 for preventing direct electrical contact between the
lower electrode element 6 and the surface to be contacted. The
insulating cap 13 may be in the form of a steel plate covered by a
polyvinyl chloride film.
The upper portion of lower electrode element 6 forms an extruded
and exposed portion 6a which is located within a central,
downwardly opening socket in the upper electrode element 7. As with
the conventional electrode shown in FIG. 1, in the electrode 20 of
FIG. 2, the upper electrode element 7 is affixed to the lower
electrode element 6 by crimping in the area 8 of the upper
electrode element 7.
The upper electrode element 7 is formed with a flange portion 7a
extending radially out from the central socket of element 7. A
ring-shaped solder layer 14 is located between flange portion 7a
and conductive substrate 11 around lower electrode element 6. In
the construction of the electrode 20, the ring-shaped solder layer
14 may initially be in the form of a washer of solder material
which is first assembled into the electrode and then melted,
thereby becoming affixed to and forming good electrical contact
between the upper electrode element 7, the lower electrode element
6 and the conductive substrate 11. As a result, it is possible to
unite the solder material of the solder washer 14 with the
electrode element 7 and to impregnate the solder material into the
conductive substrate 11 for achieving an anchoring effect. The
shading on FIG. 6 illustrates the resulting solder dispersal
achieved when the upper element 7 is crimped to attach elements 6
and 7, right after or while being heated to melt the solder. The
solder washer 14 may comprise a solder material having a melting
point of more than 60.degree. C. Alternatively, the layer 14 may be
formed by a conductive paint or a solder paste which is printed or
otherwise applied on conductive substrate 11 before the electrode
elements 6 and 7 are united. In this case, no further heating is
required because the anchoring effect on the conductive substrate
11 is achieved when printing the conductive paint or the solder
paste. However, when solder paste is used, it is preferable to
improve the contact between the particles of the solder paste by
the subsequent heating thereof.
FIG. 5 illustrates the relation of the components of electrode 20
just prior to assembly. The contacting portions including the
conductive substrate 11 and the adhesive layer 12 are separately
manufactured as described below. The eyelet-like elements 6 and 7
are disposed to penetrate the substrate 11 and adhesive layer 12
through the hole 18 with the solder washer 14 disposed
therebetween.
When, as described above, the solder layer 14 is tightly united
with upper electrode element 7 while being partly impregnated in
the conductive substrate 11 to effectively contact the conductive
fibers contained in the latter, the upper electrode element 7 can
be electrically well connected with the conductive substrate 11. As
a result, a sufficient electrical contact can be obtained and the
electric resistance of the electrode can be reduced to effectively
prevent the concentration of electric current.
In the conventional electrode of FIG. 1, the elements 6 and 7 are
held in assembled relation only by crimping at 8, whereas, in the
electrode 20 according to this invention, the elements 6 and 7, in
addition to being crimped together, are soldered to the conductive
substrate 11 to provide a stable attachment to the latter and
superior mechanical strength.
It is preferable that the lower electrode element 6 have the
ring-shaped flange 6b at the end which is to face forward the
living body and that the separate washer 19 of metal be disposed
between the flange 6b and the conductive adhesive 12 to prevent
detachment or deviation of the lower electrode element 6 in respect
to the conductive substrate. The flange 6b of element 6 can be
provided with the insulating cap 13 engaging therearound or with an
insulating film as fixed thereon by an adhesive, to prevent
concentrations of electric currents to the living body.
In the electrode 20 of FIG. 2, the sponge-like substrate 1, which
may consist of an insulating material, is affixed by adhesive layer
2 to conductive substrate 11, at the side of the latter opposite
the adhesive layer 12. The lead wire or grounding cable 15 is
attached through terminal plate 16 to the upper electrode element 7
to form with solder layer 14 a means for electrical connection to
the conductive substrate 11. The electrode 20 of FIG. 2 is also
shown to have a stripable piece of sanitary paper 17 affixed by
adhesive layer 12 to the surface of the latter for maintaining the
contact area of the adhesive layer 12 in a sanitary condition. The
paper 17 is normally removed just prior to application of the
electrode element to the surface area of the living body to be
contacted.
As previously mentioned, the conductive substrate 11 of the
electrode 20 according to the present invention is of a textile
containing conductive fibers. Such conductive substrate may be a
textile formed only of carbon fibers or only of metal fibers, for
example, of copper, silver, stainless steel or the like. The
conductive substrate can be constituted by a textile formed of a
mixture of metal fibers and organic fibers, or a mixture of metal
fibers and insulating inorganic fibers, such as, glass fibers. In
the latter case, warp and woof of the textile may be woven by
turns. In either case, it is preferable that at least 15% by
weight, and most desirably, at least 20%, by weight, of the textile
is formed of conductive fibers. When the textile forming the
conductive substrate is of a mixture of fibers, the conductive
fibers should uniformly appear on a surface of the respective yarn.
The conductive fibers are accordingly distributed almost uniformly
on a surface of the textile so that the specific resistance of the
textile becomes uniform. With such construction it has been found
that the conductive substrate 11 can be made to have a specific
resistance, or resistivity of less than 100.OMEGA. cm.
In addition, it is preferable that the conductive substrate 11 have
a thickness of 50 to 1000 .mu.m., with a thickness of approximately
500 .mu.m, being most preferred. The lower limit ensures that the
conductive substrate will have sufficient tensile strength and the
upper limit is determined to provide sufficient flexibility for
conforming to the various curved surfaces found on a living
body.
In one specific embodiment of the invention, conductive substrate
11 comprises a mixed textile of 20% metal fibers of stainless steel
and 80% polyester fibers and has a tensile strength of 150 kg, a
cutting extensibility of no more than 32%, a shrinkage percentage
of 0.5% and a crease-proof precentage of more than 79%, all in the
longitudinal direction of its weave. Such substrate 11 also has a
tensile strength of 68 kg, a cutting extensibility of no more than
33%, a shrinkage percentage of 0% and a crease-proof percentage of
more than 83%, in the lateral direction of the weave. The specific
resistance of such a substrate is, for example, 60.OMEGA. cm. The
metal fibers of the substrate are, for example, 8 .mu.m in
diameter. When the diameter of the metal fiber is too large, the
yarns of the mixed textile tend to be hardened and the flexibility
of the textile is deteriorated.
As previously mentioned, the adhesive layer 12 of electrode 20
according to the present invention contains carbon fibers, with
such carbon fibers being entwined to contact each other and also
appear on the surface of the layer 12. As a result, an electric
resistance of the adhesive layer 12 can be relatively low and
uniform. It is preferable that the carbon fibers contained in the
adhesive layer 12 have a length of 0.2 to 6 mm. When the length of
the carbon fibers is less than 0.2 mm, the interconnection effect
resulting from the entwining of the carbon fibers is poorer. When
the length of the carbon fibers is over 6 mm, the carbon fibers
cannot be well dispersed in the resin and the adhesive cannot be
well coated on the substrate 11. It is preferable that the diameter
of the carbon fibers be 1 to 20 .mu.m, because the conductivity is
poorer when the diameter is less than 1 .mu.m, and the dispersion
of the carbon fibers in the resin and the coating property of the
adhesive on the substrate are degraded when the diameter is over 20
.mu.m. In addition, it is preferable that the content of the carbon
fibers in the adhesive layer 12 be 2 to 30%, by weight, relative to
the amount of the resin in the adhesive layer because the
conductivity is poorer when the carbon fiber content is less than
2%, and the adhesive force of the adhesive layer is degraded due to
decrease of the proportion of the resin when the carbon fiber
content is over 30%. It is necessary that the conductive adhesive
layer 12 have a specific resistance of no more than 100.OMEGA. cm.
By way of example, when carbon fibers having a diameter of 7 .mu.m
are used, it is particularly preferable that 3% by weight of the
carbon fibers be used if the latter have a length of 6 mm, that 5%
by weight of the carbon fibers be used if the latter have a length
of 3 mm., that 7.5 to 10% by weight of the carbon fibers be used if
the latter have a length of 1 mm., and that 25% by weight of the
carbon fibers be used if the latter have a length of 0.5 mm.
The adhesive layer 12 preferably has a thickness of more than 25
.mu.m to ensure that the adhesive force will have a desired value.
The thickness of the adhesive layer, in practice, is up to 200
.mu.m, and is preferably around 100 .mu.m. This upper limit is
required from the point of view of mechanical strength of the
adhesive layer in use.
To form the adhesive layer 12, a cross-linking agent may be
dissolved into a diluent and a base polymer, as the resin part, is
mixed into the resulting solution. As a result, the base polymer is
partly cross-linked by the cross-linking agent. Carbon fibers are
then dispersed into the solution of the cross-linked base polymer.
The solution having the dispersed carbon fibers is uniformly coated
on a paper capable of being peeled off and the solvent of the
solution is evaporated. At this time, uncross-linked portions of
the base polymer are cross-linked so that an almost completely
cross-linked adhesive resin layer containing the carbon fibers is
obtained. The previously described conductive substrate 11 is then
laminated on the adhesive resin layer 12. The laminated sheet
comprising the adhesive resin layer 12 and the conductive substrate
11 is then cut in a die press to produce an electrode 20 having a
given size and shape.
The base polymer of the resin forming adhesive layer 12 in the
electrode 20 according to the present invention will be now
explained. It is preferable that a major part of the monomers of
the base polymer consist of acrylic acid esters or methacrylic acid
esters of an alcohol having 1 to 8 carbon atoms in its molecule,
and a minor part of the monomers consist of vinyl compounds having
a crosslinkable functional group.
Examples of the above acrylic acid esters are methyl acrylate,
ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl
acrylate, tertiary butyl acrylate , amyl acrylate, n-hexyl
acrylate, cyclohexyl acrylate, 2-ethyl hexyl acrylate and the like.
Examples of the above methacrylic acid esters are methyl
methacrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl
methacrylate, n-amyl methacrylate, 3-methyl-pentyl methacrylate,
n-hexyl methacrylate, 2-methyl hexyl methacrylate, 2-ethyl hexyl
methacrylate, n-heptyl methacrylate, n-octyl methacrylate and the
like.
A portion of the acrylic or methacrylic acid ester of an alcohol
having 1 to 8 carbon atoms may be substituted by another kind of
vinyl compound, such as, acrylic or methacrylic acid ester having 9
to 18 carbon atoms, vinyl chloride, vinyl propionate, acrylonitrile
or vinyl acetate. In such case, less than 20 parts, by weight, and
preferably less than 10 parts, by weight, for each 100 parts, by
weight, of the acrylic or methacrylic acid ester of alcohol of 1 to
8 carbon atoms may be replaced or substituted by the other kind of
vinyl compound.
The vinyl compound having a crosslinkable functional group must be
copolymerized in the base polymer in the range of 0.25 to 3.0
parts, by weight, for each 100 parts by weight of the total amount
of the base polymer. The crosslinkable functional group of the
vinyl compound (monomer) may be a carboxyl group, hydroxyl group,
amino group, amido group or epoxy group. Examples of these vinyl
compounds are acrylic acid, methacrylic acid, crotonic acid, maleic
acid, itaconic acid 2-hydroxyethylacrylate,
2-hydroxypropylacrylate, 2-hydroxyethylmethacrylate,
2-hydroxypropylmethacrylate, acrylamide, methacrylamide,
N-methylolacrylamide, N-mehtylolmethacrylamide, glycidylacrylate
and glycidylmethacrylate.
When the base polymer is produced by copolymerization with less
than 0.25 parts by weight of the crosslinkable monomer, an
electroconductive pressure-sensitive adhesive layer comprising such
a base polymer has an undesired low mechanical strength. On the
other hand, a base polymer with more than 3.0 parts by weight of
the crosslinkable monomer is apt to gelantinize and therefore is
not suitable for being coated on the substrate. The base polymer
suitable for the present invention has a glass transition
temperature in the range from -85.degree. to 0.degree. C. and has
an average molecular weight in the range from 50,000 to 500,000,
from the point of view of pressure-sensitive adhesivity.
The base polymer used for the present invention can be synthesized
by any one of the following four methods:
According to the first method, 70 parts by weight of
2-ethylhexylacrylate, 30 parts by weight of n-butylacrylate, 2.5
parts by weight of acrylic acid and 0.5 parts by weight of
azobisisobutyronitrile (a polymerization initiator) are
respectively dissolved into ethyl acetate (a polymerization
solvent). In this case, the ratio of the polymerizable constituents
and the polymerization initiator to the polymerization solvent is
1:1. The polymerizable constituents are then polymerized at a
polymerization temperature of 50.degree. to 60.degree. C. for 8
hours. The resulting polymer is diluted by adding toluene (a
diluent) to obtain a base polymer solution having a viscosity of
3925 cps.
In accordance with the second method, in which the same kinds and
amounts of polymerization constitutents and polymerization
initiator are used as in the first method, except 1.0 parts by
weight of glycidylmethacrylate are used in place of acrylic acid
for polymerization under the same conditions and a base polymer
solution having a viscosity of 750 cps is obtained after the
dilution of the polymer.
In the third method, in which the same kinds and amounts of
polymerization constituents and polymerization initiator are used
as in the first method, except 3.1 parts be weight of
.beta.-hydroxylethylmethacrylate are used in place of acrylic acid
for polymerization under the same conditions, and a base polymer
solution having a viscosity of 900 cps is obtained after the
dilution of the polymer.
In the fourth method, 70 parts by weight of 2-ethylhexylacrylate,
70 parts by weight of n-butylacrylate, 2.5 parts by weight of
acrylic acid and 0.3 parts by weight of glycidylmethacrylate are
used as polymerization constituents. These constituents are
polymerized by the use of 0.5 parts by weight of
azobisisobutyronitrile under the same conditions as in the first
method. The base polymer solution thus obtained has a viscosity of
1350 cps after the dilution of the polymer.
The base polymer produced by any one of the above methods is
cross-linked by a cross-linking agent to form adhesives having a
desired adhesive force. The cross-linking agent can be Tyzor A.A.
(titanium chelate compound of acetyl acetone) manufactured by E. I.
Du Pont Corp., ALCH (ehtyl acetate aluminum diisopropoxide),
chelate compound of phenol resin and MgO and the like. The
cross-linking agent reacts with the crosslinkable functional group
of the base polymer, such as, the carboxyl group of acrylic acid,
oxirane (ethylene oxide) group of glycidylmethacrylate and hydroxyl
group of .beta.-hydroxyethylmethacrylate. The solution of Tyzor
A.A. as a cross-linking agent with a concentration of 1% is
preferably used at a rate of 0.25 to 20.0 parts by weight relative
to 25 parts by weight of the base polymer. The solution of ALCH as
a cross-linking agent with a concentration of 1% is preferably used
at a rate of about 2.0 parts by weight relative to 25 parts by
weight of the base polymer. MgO chelate is preferably used at a
rate of 0.25 to 1.0 parts by weight relative to 100 parts by weight
of the base polymer. If the amount of the respective cross-linking
agent is out of the previously indicated range therefor, that is,
when the amount is too little, the thermal creep of the base
polymer is deteriorated and, when the amount is too much, the base
polymer is liable to gelatinize. When the cross-linking agent is
used in a suitable amount, the thermal creep is more than 120
minutes and is remarkably improved in comparison with the thermal
creep of a few seconds which is encountered without using a
cross-linking agent.
The adhesive used in the conductive adhesive layer 12 of the
present invention can be a natural rubber rather than the
above-described adhesive resin comprising acrylic polymer and
cross-linking agent. For example, 100 parts by weight of natural
rubber of pale crepe which has been sufficiently masticated by an
open roll may be dissolved into 500 weight parts of toluene. The
resulting solution then has added thereto 90 parts by weight of
zinc oxide, 50 parts by weight of polyisoprene (Picopal 100 SF
manufactured by Esso Standard Petroleum Corp.), 24 parts by weight
of carbon fibers having a diameter of 7 .mu.m and a length of about
1 mm(Torayca manufactured by Toyo Rayon Corp.) which is produced by
burning acrylonitrile fibers to carbonize and then subjecting the
carbonized fibers to a heat treatment to graphitize.
The electrode 20 embodying this invention may be used in the manner
shown on FIG. 7. More particularly, the electrode 20 may be fixed
on the thigh or back of a patient 22 on an operating table 21 and
the grounding cable 15 from the electrode 20 is led to an electric
surgical unit 23. An active surgical electrode 25, or
electro-surgical pencil with blade, is connected to the end of an
active cable 24 extending from the unit 23 and is held by a
surgeon. The active surgical electrode 25 is applied to the
affected part of the patient. In such a condition, high-frequency
electric currents 26 are supplied to the active surgical electrode
25 by the cable 24 and then led to the electrode 20 through the
body of the patient. The high-frequency electric currents serve to
cut the affected part by burning and/or to effect coagulation of
the blood. In addition to the above, the electrode of the present
invention may also be used in connection with the making of
electro-cardiogram and brain wave measurements. The small size
permitted by the construction according to this invention is
particularly well suited to the latter of these additional
uses.
It will be evident that various modifications can be made to the
above-described embodiments without departing from the scope of the
present invention. For example, the lower eyelet electrode element
6 may be formed of an insulating material which acts only as a
supporting member for the upper electrode element 7. The electrode
elements 6 and 7 can be united by means other than the illustrated
grommet construction. The lower electrode element 6 may not be
formed with the flanged end 6b before being inserted through the
hole 18. In other words, after the lower electrode element 6 is
inserted through the hole 18 to be united with the upper electrode
element 7 by crimping the lower end of lower electrode element 6
can be bent outwards against the adhesive layer 12 to form a
ring-shaped portion like the flanged end 6b.
The electrical characteristics of an electrode according to the
present invention will now be described in relation to FIGS. 3 and
4.
FIG. 3 shows the frequency characteristics of electrodes according
to the present invention in comparison with the conventional
conductive jelly type of electrode manufactured by American
Hospital Supply Corp., with each electric resistance value for a
contacting area of 10 cm.times.10 cm being shown for each
electrode. In FIG. 3, symbols "O" show the characteristic of an
electode according to the present invention in which the conductive
substrate 11 is composed of a mixed textile containing 20%
stainless steel fibers, the symbols "X" show the characteristic of
another electrode according to the present invention in which the
conductive substrate 11 is composed of a mixed textile containing
30% copper fibers, the symbols ".DELTA." show the characteristic of
a further electrode according to the present invention in which the
conductive substrate 11 is composed of a textile of 100% carbon
fibers, and the symbols " " show the characterisitic of the
conventional electrode of the conductive jelly type. From FIG. 3 it
will be seen that the electrodes of the present invention have a
sufficiently low electric resistance of less than 100.OMEGA., for
example, in the range of 500 KHz to 25 MHz, which is a practical
frequency range for an electric surgical knife, and that the
resistance values of the electrodes according to the present
invention are lower than or substantially equal to an electric
resistance value of the conventional electrode. The electrodes
according to the present invention represented on FIG. 3 each have
the conductive adhesive layer 12 thereof produced by cross-linking
25 parts by weight of acrylic polymer obtained in the above
described first synthesizing method by 40 parts by weight of the
cross-linking agent (Tyzor A.A.) with a concentration of 1%, and
adding 10% by weight of the carbon fibers having a length of 1 mm
and a diameter of 7 .mu.m to the resulting cross-linked
polymer.
FIGS. 4A and 4B show the specific resistances or resistivities for
various conductive substrates 11 that may be included in electrodes
according to this invention. On FIG. 4A, the symbol " " shows the
specific resistance of a conductive substrate composed of 100%
stainless steel fibers, and the symbol ".DELTA." shows the specific
resistance of another conductive substrate composed of 100% carbon
fibers. On FIG. 4B, the symbol " " shows the specific resistance of
a conductive substrate composed of a mixed textile containing 20%
stainless steel fibers, the symbol " " shows the specific
resistance of a conductive substrate composed of a textile
comprising 30% carbon fibers and b 70% glass fibers, and the symbol
"X" shows the specific resistance of a conductive substrate
composed of a mixed textile containing 30% copper fibers. FIGS. 4A
and 4B show that each conductive substrate according to the present
invention has a specific resistance equal to or less than
100.OMEGA. cm. which is required for an electrode to be used as a
grounding pad in association with an electric surgical knife. It is
particularly preferable that the conductive substrate 11 be
composed of a textile of 100% stainless steel fibers or 100% carbon
fibers, as such conductive substrates have the lowest specific
resistance values.
It will be apparent that, in the above described embodiments of the
present invention, electrodes are provided with reduced electrical
resistance to effectively prevent a local concentration of electric
current. Also, the conductive substrate 11 and the ring-like solder
layer 14 act to evenly distribute the current across the surface
area of the adhesive layer 12. Additionally, the insulating cap 13
serves to insulate the lower electrode element 6 from the living
body and thereby prevent concentrations of current flow
therebetween. Another advantage of electrodes constructed according
to the present invention is a sufficient flexibility to conform to
the various concave and convex surfaces found on a living body.
With such flexibility, an electrode according to the present
invention can be contacted with the living body without forming any
wrinkles in the electrode. Another advantage of the present
invention is that the conductive substrate and adhesive layer are
not dried like the gauze or jelly used in conventional electrodes,
thereby preventing this cause of current concentration and the
related danger of burns. In addition, the electrode according to
the present invention can be easily constructed and handled from
the view point of sanitization and further can be easily
miniaturized, because the conductive adhesive layer 12 is
integrally formed with the conductive substrate 11. An additional
advantage of electrodes according to the present invention is that
the same may be constructed with a mechanical strength superior to
that of conventional electrodes.
Although illustrative embodiments of the invention have been
described in detail herein with reference to the accompanying
drawings, it is to be understood that the invention is not limited
to those precise embodiments, and that various changes and
modifications may be effected therein by one skilled in the art
without departing from the scope or spirit of the invention as
defined in the appended claims.
* * * * *